The halogen chemistry of halide perovskites

In analogy to the role of oxide anion in perovskites, halogen chemistry halide perovskites significantly contributes chemical, physical, and optoelectronic properties this class materials.Investigating manipulating site has improved our understanding electronic structure, reactivity, defect chemistry, ionic conductivity perovskites.A clear is expected (i) yield novel with targeted controlled (ii) improve efficiency stability perovskite devices, (iii) expand scope postsynthetic reactions between small molecules. The oxygen been studied for decades, revealing transport, enabled by anion. Similarly, dictates unusual phenomena observed perovskites. Manipulating performance a range technologies, most commonly as components solar cells light-emitting diodes. Further, redox activity halides allows doping exchange, well capture separation gases. Herein, we summarize key aspects site. We close discussion pseudohalide which hold commonalities Perovskites are crystalline solids general formula ABX3, where X an anionic ligand such oxide, chalcogenide, or halide. Historically, have received attention family materials. Although also not new?dating back 1800s [1.Berzelius J.J. Untersuchung über die eigenschaften des tellurs.Ann. Phys. 1834; 108: 577-627Google Scholar, 2.Cross W. Hillebrand W.F. Contributions mineralogy rocky mountains.in: Bulletin United States Geological Survey No. 20. Government Printing Office, 1885: 57Google 3.Wells H.L. Über cäsium- und kalium-bleihalogenide.Z. Anorg. Allg. Chem. 1893; 3: 195-210Google 4.Elliott N. Pauling L. crystal structure cesium aurous auric chloride, Cs2AuAuCl6, argentous Cs2AgAuCl6.J. Am. Soc. 1938; 60: 1846-1851Google Scholar]?their study recently invigorated through discovery their outstanding semiconducting properties. lead-halide emerged candidates high-efficiency low-cost absorbers [5.Kojima A. et al.Organometal visible-light sensitizers photovoltaic cells.J. 2009; 131: 6050-6051Google 6.Kim H.-S. al.Lead iodide sensitized all-solid-state submicron thin film mesoscopic cell exceeding 9%.Sci. Rep. 2012; 2: 591Google 7.Lee M.M. al.Efficient hybrid based on meso-superstructured organometal perovskites.Science. 338: 643Google Scholar], while other applications phosphors [8.Protesescu al.Nanocrystals lead (CsPbX3, = Cl, Br, I): materials showing bright emission wide color gamut.Nano Lett. 2015; 15: 3692-3696Google Scholar,9.Smith M.D. al.Tuning luminescence layered perovskites.Chem. Rev. 2019; 119: 3104-3139Google diodes [10.Chondroudis K. Mitzi D.B. Electroluminescence from organic?inorganic incorporating quaterthiophene dye within layers.Chem. Mater. 1999; 11: 3028-3030Google Scholar,11.Lin al.Perovskite external quantum 20 per cent.Nature. 2018; 562: 245-248Google scintillators [12.Chen Q. al.All-inorganic nanocrystal scintillators.Nature. 561: 88-93Google Scholar] shown promise. many defining characteristics perovskites: solution-state self-assembly, stabilization low-valent metals, soft lattices bulk moduli (see Glossary) that can be those organic molecules, structures exhibit fast slow dynamics, shallow trap states. Indeed, optimized [e.g., optical bandgap photoluminescence (PL) color, chemistry], explained perovskite-based devices (e.g., light-induced segregation mixed-halide compositions), resulted new radioactive I2 capture, gas separation). Here, compile describe dictating absorption emission, reactivity conclude briefly reviewing closely related refer interested readers recent reviews [13.Senocrate Maier J. Solid-state ionics perovskites.J. 141: 8382-8396Google photo-induced phase [14.Slotcavage D.J. al.Light-induced halide-perovskite absorbers.ACS Energy 2016; 1: 1199-1205Google Scholar,15.Brennan M.C. al.Photoinduced mixed perovskites.Trends 2020; 282-301Google [16.Li al.Chemically diverse multifunctional organic–inorganic perovskites.Nat. 2017; 16099Google [17.Smith I.C. al.Between sheets: transformations 29: 1868-1884Google Scholar]. Halide structural analogs CaTiO3. Substitutions at A- B-sites ABO3 led important electroceramics, including dielectrics piezoelectrics [18.Bhalla A.S. al.The structure—a review its ceramic science technology.Mater. Res. Innov. 2000; 4: 3-26Google Non-stoichiometry ABO3±?) point reactions, however, appreciated modern discoveries, high-temperature cuprate superconductors [19.Bednorz J.G. Müller K.A. Possible high Tc superconductivity Ba?La?Cu?O system.Z. B. 1986; 64: 189-193Google A detailed treatment afforded good bonding As members same family, parallels X-site made critical temperature (Tc) YBa2Cu3O7–? sensitive local Cu–O coordination changes induced non-stoichiometry [20.Cava R.J. Synthesis high-Tc superconductor.in: Jin S. Processing Properties High-TC Superconductors. World Scientific, 1993: 492Google Scholar]; further, interactions charge carriers defects influence upon aliovalent La2CuO4 (i.e., La2–xMxCuO4, M Ba2+, Sr2+) [21.Rao C.N.R. Perovskite oxides superconductivity.Ferroelectrics. 1990; 102: 297-308Google Scholar,22.Maier Physical Chemistry Ionic Materials: Ions Electrons Solids. John Wiley & Sons, 2004Google proposed mechanism these two involves holes forming O– (O2? + h+) O22– peroxo dimers Conversely, elevated temperatures, oxygen-vacancy–mediated transport enables solid electrolytes alloyed doped LaMO3 (M Ga3+, Al3+, In3+, Sc3+, Y3+) [23.Kharton V.V. al.Transport electrolyte ceramics: brief review.Solid State Ion. 2004; 174: 135-149Google similarly occupancy. Oxygen exchange critically reaction describes equilibrium lattice, vacancies, electrons, gaseous O22OOX?2VO••+4e?+O2g[1] OOX pristine lattice site, VO•• dicationic vacancy, e? electron (given Kröger–Vink notation). O2 partial pressure (generally >700 K) diffusion thermodynamics [22.Maier rational design complex instance promote resist informed composition-dependent kinetics thermodynamic modeling dopants. analogous particularly low activation barriers formation calling similar chemical approaches stability. Thus, uncovering congeners should deeper latter Outstanding questions). adopt 3D ABX3 feature octahedral six (X); each bridges afford BX3– framework corner-sharing octahedra. Organic and/or inorganic A-site monocations reside cuboctahedral voids, providing compensation (Figure 1A ). B occupied 2+ metal single Pb2+, Hg2+, Mn2+ [9.Smith Scholar]), whereas distinct B? sites alternate A2BB?X6 double affording average Ag+ Bi3+ Sn4+ vacancy; Figure 1B) [24.Wolf N.R. al.Doubling stakes: promise perovskites.Angew. Int. Ed. 2021; 16264-16278Google 2D formal addition AX salt (ABX3 ? A2BX4), resulting both bridging terminal sheets separated larger cations 1C) [25.Saparov Organic–inorganic versatility functional design.Chem. 116: 4558-4596Google Scholar,26.Smith diversity perovskites.Annu. 48: 111-136Google Linus Pauling’s radius ratio rules dictate size cation support given anion/cation increases, lower numbers preferred. For example, aware B-site Cd2+. However, CsCdX3 (X Cl?, Br?) KMnCl3 crystallize smaller [27.Natta G. Passerini Isomorphism, polymorphism morphotropy, I. Compounds type.Gazz. Chim. Ital. 1928; 58: 472-484Google 28.Horowitz al.Structure types TlMnCl3.J. Solid 1982; 43: 107-125Google 29.Travis al.On application tolerance factor revised system.Chem. Sci. 7: 4548-4556Google Goldschmidt [30.Goldschmidt V.M. Die gesetze der krystallochemie.Naturwissenschaften. 1926; 14: 477-485Google derived geometric considerations, identifies limits A-site–cation B-site–cation radii [31.Filip M.R. Giustino F. blueprint perovskites.Proc. Natl. Acad. U. 115: 5397-5402Google Scholar,32.Bartel C.J. al.New predict halides.Sci. Adv. 5: aav0693Google Compositions deviate ideal, undistorted perovskite, 180° B–X–B angles 1B), will either lower-symmetry tilted octahedra) 1A) non-perovskite [33.Steele J.A. al.Trojans flip black phase: impurity-driven spontaneous strain suppression ?-CsPbI3 perovskite.J. 143: 10500-10508Google effects hydrostatic temperature, composition direct preferential crystallization desired crystallographic phases. Cs-substitution induce cubic-to-tetragonal transition [CH(NH2)2]yCs1–yPb(BrxI1–x)3 films [34.Beal R.E. al.Structural origins organic-inorganic materials.Matter. 207-219Google Further increasing effective separates metal–halide This often achieved organoammonium size, charge, shape determines dimensionality (0D, 1D, 2D) connectivity (corner-, edge-, face-sharing) octahedra [26.Smith Halogen template organohalogens assembly some [35.Connor B.A. al.Dimensional reduction small-bandgap Cs2AgTlBr6.Chem. 7708-7715Google Scholar,36.Lemmerer Billing D.G. Effect heteroatoms inorganic–organic perovskite-type hybrids [(ZCnH2nNH3)2PbI4], n 2, 3, 4, 5, 6; Z OH, Br I; [(H3NC2H4S2C2H4NH3)PbI4].CrystEngComm. 2010; 12: 1290-1301Google Lighter reported preferentially occupy heavier tend [37.Suzuki Y. Kubo H. Distribution Cl- Br- ions crystals (CH3NH3)2Cu(Cl1-xBrx)4.J. Jpn. 1983; 52: 1420-1426Google Scholar,38.Sourisseau al.Hybrid solid-state layers ?1-(Br-(CH2)2-NH3)2PbI4.Inorg. 2007; 46: 6148-6154Google mainly set s-orbitals p-orbitals compose valence band, conduction band primarily comprises 2A ) [39.Umebayashi T. al.Electronic low-dimensional crystals.Phys. 2003; 67155405Google Scholar,40.Goesten M.G. Hoffmann R. Mirrors 140: 12996-13010Google presence lead, iodine, high-atomic-number elements necessitates spin–orbit coupling accurate motivated various relativistic phenomena, Rashba–Dresselhaus spin-splitting edges [41.Kepenekian M. Even Rashba Dresselhaus couplings accomplishments opportunities spintronics spin–orbitronics.J. 8: 3362-3370Google Alloying produces solutions Cl?/Br? Br?/I? evidenced powder X-ray diffraction measurements continuous expansion alloyed. spectra show shift onset compositions, although discontinuity x 0.5 (CH3NH3)Pb(BrxI1–x)3 films, attributed imperfect mixing 2B) [42.Hoke E.T. al.Reversible photovoltaics.Chem. 6: 613-617Google Because contribution increased substituting more electronegative 2A). bandgaps vary 1.5 (for iodides) 3.0 eV chlorides), compositions intermediate gaps importance halide–halide evident vacant (?), A2Sn?X6. structurally 0D, they display large dispersion. Their arises 90° across [43.Slavney A.H. al.A pencil-and-paper method elucidating structures.Chem. 10: 11041-11053Google monovalent fit cavity CH3NH3+, Cs+, CH(NH2)2+] few only contribute inducing distortions framework. Varying increase tilting BX6n? octahedra, decrease contraction [44.Yang T.-Y. significance ion lead-iodide-based photosensitizer.Angew. 54: 7905-7910Google orbital contributions counterparts but due confinement effects, photoexcitation excitons (bound electron–hole pairs) instead free carriers. Excitons manifest sharp peaks below onset. With alloying, excitonic peak shows blueshift ~2.3 pure Pb?I ~3.6 Pb?Cl PL tracks [45.Lanty al.Room-temperature tunability inhomogeneous broadening 2D-layered pseudobinary alloys.J. 2014; 3958-3963Google width used indicator variation (PEA)2PbClxBr4?x (PEA)2PbBrxI4?x (PEA phenethylammonium) Scholar,46.Kitazawa two-dimensional compounds: (C6H5C2H4NH3)2Pb(Br,I)4 (C6H5C2H4NH3)2Pb(Cl,Br)4.Mater. Eng. 1997; 49: 233-238Google narrow peaks, broader seen locally disordered change potential energy landscape sampled exciton. Most intense, purity, promising phosphor applications, modulating (PEA)2PbX4, I? green light, Br? yields blue light. Certain emit broadband white light [47.Smith Karunadasa H.I. White-light perovskites.Acc. 51: 619-627Google Here too, tune rendering index (CRI) correlated (CCT) emission. prototypical white-light–emitting (N-MEDA)PbClxBr4–x (N-MEDA N1-methylethane-1,2-diammonium), CRI was 82 (x 0) 85 0.5) isostructural [48.Dohner E.R. al.Self-assembly white-light emitters.J. 136: 1718-1721Google Likewise, chloride bromide derivatives (EDBE)PbX4 "cold" (CCT 5509 "warm" 3990 respectively, here adopts flat (001) corrugated (110) [49.Dohner al.Intrinsic 13154-13157Google Many highlighted require significant conductivity, where, unlike there no layer facilitate volume expansion. invoked explain anomalous behavior current–voltage hysteresis [50.Snaith H.J. al.Anomalous 1511-1515Google Scholar,51.Meloni al.Ionic polarization-induced CH3NH3PbX3 cells.Nat. Commun. 10334Google switchable [52.Xiao Z. al.Giant effect trihalide devices.Nat. 193-198Google low-frequency dielectric responses Scholar,53.Juarez-Perez E.J. giant constant 2390-2394Google Scholar,54.Wilson J.N. al.Dielectric ferroic perovskites.APL 5079633Google bending alignment interfaces [55.Bertoluzzi al.Mobile concentration measurement open-access diagram simulation platform cells.Joule. 109-127Google Scholar,56.Lopez-Varo P. al.Effects distributions collection cells.ACS 1450-1453Google semiconductors varying degrees owing disorder mobility IA,B Box 1). ionic-electronic established 1980s [57.Mizusaki halides.Solid 203-211Google initial work antiperovskite exhibiting data suggesting displacements Mizusaki colleagues CsPbX3 vacancies mobile species gravimetric coulometric IC,D (Ea) vacancy migration relatively Br?; 0.25-0.29 eV) (0.39 later suggested (CH3NH3)MCl3 Ge2+, Sn2+) [58.Yamada al.Chloride conductor CH3NH3GeCl3 Rietveld analysis 35Cl NMR.Solid 1995; 79: 152-157Google Scholar,59.Yamada al.Phase electric ASnCl3 (A Cs CH3NH3).Bull. 1998; 71: 127-134Google (CH3NH3)PbX3 [60.Maeda studies Cl Br) crystals.J. 66: 1508-1511Google (CH3NH3)PbI3 had extensively discussed Scholar,52.Xiao Scholar,61.Azpiroz J.M. al.Defect methylammonium operation.Energy Environ. 2118-2127Google were directly revisited until 2015 Maier, Gregori, Polycrystalline exhibits dark iodine dominant ID 1) Scholar,44.Yang Iodine confirmed dependencies [p(I2)] acceptor doping, NMR Scholar,62.Senocrate nature iodide: multimethod approach.Angew. 56: 7755-7759Google Scholar,63.Senocrate al.Slow CH3NH3+ CH3NH3PbI3 under measured tracer diffusion.J. C. 122: 21803-21806Google Scholar].Box 1Halogen perovskitesSeveral ionic–electronic conductors. These energies greater than 1 main text); thus, electrical derives intrinsic carrier concentrations IA, left) modified doping. donors generates excess (n-type doping; middle), acceptors generate hole (p-type right). Bulk defects, well-established relationship (X–) loss results positively charged defect, must compensated another (holes electrons). Among possible vacancy–based off-gassing (positively electrons; IB, top left), Schottky vacancies; right), anti-Frenkel negatively interstitials; bottom) focus investigation occurs follow vacancy-assisted hopping IC). using electrochemistry techniques, electrolysis CsPbBr3 ID, top) CsPbCl3 (identical construction CsPbBr3;